The impact of the magnitude 7.8 earthquake that struck Mindanao this week spilled over into the power sector on Wednesday, prompting the National Grid Corp. of the Philippines (NGCP) to place the Mindanao Grid under a Yellow Alert for the first time this year and the Visayas Grid under a Red Alert amid reduced generation capacity and lower power imports.

In an advisory issued Wednesday morning, the transmission operator declared a Yellow Alert over the Mindanao Grid from 12 noon to 3 p.m.

The alert was triggered by the tripping of GNPower Kauswagan Ltd. Co. Unit 4, the continued outage of several major coal-fired power plants affected by the earthquake, the unavailability of Filinvest Development Corp. Unit 3, and higher demand projections.

Available capacity in Mindanao stood at 2,731 megawatts (MW), against a projected peak demand of 2,611 MW. Meanwhile, 1,259.9 MW remained unavailable due to forced outages and derated plant operations.

The alert came as NGCP continued efforts to restore transmission facilities damaged by the earthquake in parts of Southwestern Mindanao.

As early as Monday night, the grid operator reported that transmission services had been partially restored in General Santos City, South Cotabato, and Sarangani, while power transmission in all other affected areas had already been fully restored.

“NGCP continues to restore the remaining affected transmission lines in Southwestern Mindanao, near the epicenter of the 7.8-magnitude earthquake,” the company said.

The disruption also reverberated across the Visayas Grid, which was placed under Red Alert from 1 p.m. to 7 p.m. and under Yellow Alert from 7 p.m. to 9 p.m.

NGCP said the Red Alert was partly driven by reduced power imports from Mindanao through the high-voltage direct current (HVDC) interconnection.

Available capacity in the Visayas reached 2,429 MW, only slightly above the projected peak demand of 2,421 MW.

The grid operator said eight power plants were on forced outage this month, while several others had remained offline since previous months and years.

An additional 12 plants were operating at reduced capacity, resulting in a total of 890.4 MW of unavailable capacity.

“A red alert status is issued when power supply is insufficient to meet consumer demand and the transmission grid’s regulating requirement,” NGCP said. “A yellow alert is issued when the operating margin is insufficient to meet the transmission grid’s contingency requirement.”